>>... a reverse biased capacitor is slightly non-linear.
>>
>> Just take your ohmmeter to an electrolytic cap.
>> One way you get 10's of megohms, the other polarity, low megs.
>> Clearly they have different DC resistances since electrochemistry
>> can still happen at the sub 1 volt level.

>I believe you are saying an electrolytic capacitor could be used as a 
>rectifier.

Not a very useful one, or a very good one, or probably a very permanent one. 
But it would work as rectifier of sorts under certain conditions. The effect 
is caused by chemical reactions which reverse direction when polarity is 
reversed. Reverse polarity will destroy the electro-chemical cell formed.

> Is this the reason I occasionally see a pair of them in series with - to - 
> in audio schematics?

It's related. They are not attempting to utilise the "diode" effect but 
rather to overcome its bad effects.

By placing 2 polarised electrolytic capacitors in series with opposed 
polarity you get a capacitor which is non polar. While the fine points of 
this mechanism are obscure it actually does seem to work reasonably well in 
practice. I've even read of people using it to produce mains voltage 
non-polarised caps for use in converting a single phase induction motor into 
an alternator. Two "mickey mouse" ideas combined to produce an apparently 
successful result.

> It always leaves me with some doubt.

It should :-) There's a degree of black art involved.



        RM


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